1. Field of the Invention
The present invention relates to an apparatus for correcting the quantity of light from an optical printer in which unevenness of the respective luminous elements is reduced to make the printing density homogeneous.
2. Description of the Prior Art
An optical printer in which a plural number of LED's (light-emitting diodes) are arranged in the form of a matric to form a known LED dot array is provided with an LED lighting circuit as shown in FIG. 4. In the drawing, a shift register 1 to which lighting data are applied, the latch circuit thereof 2, and the driving transistor Tr of an LED 3 are connected to a power source Vcc.
The shift register 1 and the latch circuit 2 are provided in a number according to those of the LED dots and the shift register 1 contains the lighting data which are temporarily memorized. When a set signal is applied thereto, the data signal of the shift register 1 is applied to the transistor Tr which is the driving portion of the LED 3 to turn the LED on. When a reset signal is applied to the latch circuit 2, the LED 3 is turned off. FIG. 5 illustrates one example of the lighting data. The data correspond, as illustrated in the drawing, to the dot number (n+1, n, and n-1) and applied thereto by the number of times of m as illustrated in FIG. 6, so the above m operations are repeated.
If the lighting data of the n-th LED 3.sub.n indicate [1] at the first and second lighting and [0] at the third and later lighting, the LED 3.sub.n is turned ON for the periods of [t.sub.1 ] and [t.sub.2 ]. Because the quantity of the luminous energy of the LED is the product of the light-emitting output (W) and the lighting time (t), unevenness of the quantity of light from the respective LED can be corrected by varying the lighting time as described above.
However, conventional apparatus for correcting the quantity of light as described above requires preparation of new data which are previously synthesized and processed for the lighting data and the correcting data, rendering the apparatus complex. In addition, the synthesized data must be repeated several times, so that there are no problems of requirement of much time for calculation and impossibility of high-speed printing. Such a conventional apparatus is shown in U.S. Pat. No. 4,455,562.